Despite the abundance of experimental knowledge, the real performance of the sino-aortic reflex system in intact organisms still remains difficult to identify. This proposal aims at achieving such an identification. We approach the problem by both experimental studies on reflex controls of largely lumped CV subsystems and model simulation (i.e., analysis by synthesis). Both outputs will be closely correlated in sequential steps as follows: 1) Acute experiments in anesthetized dogs fill in the information gaps such as the reflex controls of cardiac pressure-volume relationship and systemic and pulmonary vascular capacities. The results and earlier findings are put in an initial crude but complete model under a set of simplifying assumptions. 2) The study then moves to estimation of the parametric controls of all the major components of circulation in intact dogs. Initially, just the sinus and/or aortic receptors are perturbed in conscious dogs by head level change, neck suction and aortic constriction with implanted cuffs. 3) The measured hemodynamic data are compared with the crude model's responses to the same perturbances. The difference revises some of the hypotheses, model parameter values, or both. In turn, the model, now adjusted to the real system, permits estimation or reflex changes in some of the plant parameters unmeasurable in intact dogs. The study repeated after anesthetizing the same dogs defines the modifications of the reflex performance by anesthesia. 4) Finally, a group of dogs are hemorrhaged, first in conscious and then anesthetized conditions. The data are compared with the revised model's output, revealing the reflex performances peculiar to hemorrhage. Whether the variation among subjects derives from the reflex system or the cardiovascular plant will also be analyzed as far as possible. Through the sequential interactions between the experiment and modelling, realistic pictures of the reflex performance in intact animals are expected to emerge.